Partners' Capital Notes [Abstract] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] Kilroy Realty L.P. [Member] Kilroy Realty L.P. [Member] Kilroy Realty L.P. [Member] Non-affiliated investors and certain of our executive officers and directors [Member] Non-Affiliated Investors [Member] Non-Affiliated Investors And Executive Officers And Directors [Member] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Common units [Member] Capital Units [Member] Ownership [Axis] Ownership [Axis] Ownership [Domain] Ownership [Domain] Operating Partnership [Member] Operating Partnership [Member] Operating Partnership [Member] Class of Stock [Line Items] General Partners' Capital Account [Abstract] Company owned common units in the Operating Partnership General Partners' Capital Account, Units Outstanding Ownership interest Limited Liability Company or Limited Partnership, Members or Limited Partners, Ownership Interest Noncontrolling common units of the Operating Partnership Limited Partners' Capital Account, Units Outstanding Earnings Per Share [Abstract] Net income available to common stockholders Net Income (Loss) Available to Common Stockholders, Diluted [Abstract] Numerator: Numerator [Abstract] Numerator. Net income attributable to Kilroy Realty Corporation Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Allocation to participating securities Participating Securities, Distributed and Undistributed Earnings (Loss), Basic Numerator for basic and diluted net income available to common stockholders Net Income (Loss) Available to Common Stockholders, Basic and Diluted Net income (loss) after adjustments for preferred distributions and dividends and allocations to participating securities. Denominator: Earnings Per Common Unit, Denominator [Abstract] Earnings Per Common Unit - Denominator Basic weighted average vested shares outstanding (in shares) Weighted Average Number of Shares Outstanding, Basic Effect of dilutive securities (in shares) Weighted Average Number Diluted Shares Outstanding Adjustment Diluted weighted average vested shares and common stock equivalents outstanding (in shares) Weighted Average Number of Shares Outstanding, Diluted Basic earnings per share: Earnings Per Share, Basic [Abstract] Net income available to common stockholders per share (in dollars per share) Earnings Per Share, Basic Diluted earnings per share: Earnings Per Share, Diluted [Abstract] Net income available to common stockholders per share (in dollars per share) Earnings Per Share, Diluted Debt Disclosure [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Debt Instrument [Line Items] Debt Instrument [Line Items] Unsecured revolving credit facility Schedule of Line of Credit Facilities [Table Text Block] Schedule of debt maturities Schedule of Maturities of Long-term Debt [Table Text Block] Capitalized interest and loan fees Capitalized Interest And Loan Fees [Table Text Block] Capitalized interest and loan fees. Organization, Consolidation and Presentation of Financial Statements [Abstract] Schedule of Real Estate Properties [Table] Schedule of Real Estate Properties [Table] Major Property Class [Axis] Major Property Class [Axis] Major Property Class [Domain] Major Property Class [Domain] Stabilized office properties [Member] Office Properties [Member] Office Properties [Member] Stabilized residential properties [Member] Stabilized Residential Properties [Member] Stabilized Residential Properties [Member] In-process development projects - tenant improvement [Member] Development Projects - Tenant Improvement [Member] Development Projects - Tenant Improvement [Member] In-process development projects - under construction [Member] Development Projects - Under Construction [Member] Development Projects - Under Construction [Member] Completed residential development project [Member] Residential development project [Member] Residential development project [Member] Real Estate Properties [Line Items] Real Estate Properties [Line Items] Number of Buildings Number of Real Estate Properties Rentable Square Feet Net Rentable Area Number of Tenants Number Of Tenants Number of Tenants. Percentage Occupied Real Estate Properties, Percentage Occupied Real Estate Properties, Percentage Occupied Percentage Leased Real Estate Properties, Percentage Leased Real Estate Properties, Percentage Leased Number of Units Number of Units in Real Estate Property Number of residential units Number of Residential Units Number of Residential Units Partners’ Capital of the Operating Partnership Partners' Capital Notes Disclosure [Text Block] Secured and Unsecured Debt of the Operating Partnership Debt Disclosure [Text Block] Statement of Cash Flows [Abstract] Statement [Table] Statement [Table] Statement [Line Items] Statement [Line Items] CASH FLOWS FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and amortization of real estate assets and leasing costs Depreciation, Depletion and Amortization Depreciation of non-real estate furniture, fixtures and equipment Depreciation, Non Real Estate Assets Depreciation, Non Real Estate Assets Revenue reversals (recoveries) for doubtful accounts Provision for Doubtful Accounts, Including Tenant’s Lease Agreement Provision for Doubtful Accounts, Including Tenant’s Lease Agreement Non-cash amortization of share-based compensation awards Share-based Payment Arrangement, Noncash Expense Non-cash amortization of deferred financing costs and debt discounts and premiums Amortization of Debt Issuance Costs and Discounts Non-cash amortization of net below market rents Amortization of above and below Market Leases Non-cash amortization of deferred revenue related to tenant-funded tenant improvements Noncash amortization of deferred revenue related to tenant-funded tenant improvements The amortization of deferred revenue related to tenant funded tenant improvements during the period. Amortization of deferred revenue related to tenant funded tenant improvements is additional rental income over the term of the related lease and is added back to net income when calculating cash provided by (used in) operations using the indirect method. Straight-line rents Straight Line Rent Amortization of right of use ground lease assets Operating Lease, Right-of-Use Asset, Amortization Operating Lease, Right-of-Use Asset, Amortization Net change in other operating assets Increase (Decrease) in Operating Assets Net change in other operating liabilities Increase (Decrease) in Operating Liabilities Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities CASH FLOWS FROM INVESTING ACTIVITIES: Net Cash Provided by (Used in) Investing Activities [Abstract] Expenditures for development properties and undeveloped land Payments to Develop Real Estate Assets Expenditures for operating properties and other capital assets Payments for Capital Improvements Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities CASH FLOWS FROM FINANCING ACTIVITIES: Net Cash Provided by (Used in) Financing Activities [Abstract] Net proceeds from issuance of common stock (Note 4) Proceeds from Issuance or Sale of Equity Borrowings on unsecured revolving credit facility (Note 3) Proceeds from Long-term Lines of Credit Repayments on unsecured revolving credit facility (Note 3) Repayments of Long-term Lines of Credit Principal payments and repayments of secured debt (Note 3) Repayments of Secured Debt Financing costs Payments of Financing Costs Repurchase of common stock and restricted stock units Payment, Tax Withholding, Share-based Payment Arrangement Distributions to noncontrolling interests in consolidated property partnerships Payments to Noncontrolling Interests Dividends and distributions paid to common stockholders and common unitholders Payments of Ordinary Dividends, Common Stock Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Net increase (decrease) in cash and cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Cash and cash equivalents and restricted cash, beginning of period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash and cash equivalents and restricted cash, end of period Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract] Prepaid expenses and other assets, net Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Table Text Block] Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Earnings Per Unit [Abstract] Net Income Available To Common Unitholders [Table] Net Income Available to Common Unitholders. Net Income Available To Common Unitholders [Line Items] Net Income Available To Common Unitholders [Line Items] Net Income Available To Common Unitholders. Net income available to common stockholders Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Supplemental Cash Flow Elements [Abstract] RECONCILIATION OF CASH AND CASH EQUIVALENTS AND RESTRICTED CASH: Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Restricted cash Restricted Cash and Cash Equivalents Cash and cash equivalents and restricted cash Leases [Abstract] Rental Income and Future Minimum Rent Lessor, Operating Leases [Text Block] Subsequent Events [Abstract] Subsequent Events Subsequent Events [Text Block] Subsequent Event [Table] Subsequent Event [Table] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] 4.27% Unsecured Senior Notes [Member] 4.27% Unsecured Senior Notes [Member] 4.27% Unsecured Senior Notes [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Senior Notes [Member] Senior Notes [Member] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent event [Member] Subsequent Event [Member] Subsequent Event [Line Items] Subsequent Event [Line Items] Payment of dividends Payments of Dividends Private placement debt offering amount Debt Instrument, Face Amount Debt Instrument, Interest Rate, Stated Percentage Debt Instrument, Interest Rate, Stated Percentage Fair Value Disclosures [Abstract] Fair value of the company's marketable securities Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Net gain (loss) on marketable securities Realized Gain (Loss) on Investments [Table Text Block] Carrying value and fair value of company's remaining financial instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Long-term Purchase Commitment [Table] Long-term Purchase Commitment [Table] Lease Extension Options [Axis] Lease Extension Options [Axis] Lease Extension Options [Axis] Lease Extension Options [Domain] Lease Extension Options [Domain] Lease Extension Options [Domain] Ten year ground lease extension option [Member] Ten Year Ground Lease Extension Option [Member] Ten Year Ground Lease Extension Option [Member] Forty-five year ground lease extension option [Member] Forty-Five Year Ground Lease Extension Option [Member] Forty-Five Year Ground Lease Extension Option [Member] Environmental Remediation Contingency [Axis] Environmental Remediation Contingency [Axis] Environmental Remediation Contingency [Domain] Environmental Remediation Contingency [Domain] Environmental matters [Member] Environmental Matters [Member] Environmental Matters [Member] Long-term Purchase Commitment [Line Items] Long-term Purchase Commitment [Line Items] Commitments for contracts and executed leases, operating and redevelopment and development properties Other Commitment Number of extension options Number of Ground Lease Extension Options Number of extension options on ground lease. Ground lease extension option term Ground Lease Extension Option, Period Ground Lease Extension Option, Period Weighted average discount rate, ground leases Operating Lease, Weighted Average Discount Rate, Percent Weighted average remaining lease term Operating Lease, Weighted Average Remaining Lease Term Variable lease, cost Variable Lease, Cost Accrued environmental remediation liabilities Accrual for Environmental Loss Contingencies Statement of Financial Position [Abstract] Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Common stock, shares authorized (in shares) Common Stock, Shares Authorized Common stock, shares issued (in shares) Common Stock, Shares, Issued Common stock, shares outstanding (in shares) Common Stock, Shares, Outstanding General partner, units issued General Partners' Capital Account, Units Issued General partners, units outstanding Limited partners, units issued Limited Partners' Capital Account, Units Issued Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Carrying value [Member] Reported Value Measurement [Member] Fair value [Member] Estimate of Fair Value Measurement [Member] Secured debt [Member] Secured Debt [Member] Unsecured debt [Member] Unsecured Debt [Member] Line of credit [Member] Line of Credit [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Fair value (level 2) [Member] Fair Value, Inputs, Level 2 [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair value of debt, net Debt Instrument, Fair Value Disclosure Net Income Available To Common Unitholders [Table] Net Income Available to Common Unitholders Per Unit of the Operating Partnership Earnings Per Share [Text Block] Other Significant Noncash Transactions [Table] Other Significant Noncash Transactions [Table] Other Significant Noncash Transactions [Line Items] Other Significant Noncash Transactions [Line Items] SUPPLEMENTAL CASH FLOWS INFORMATION: Supplemental Cash Flow Information [Abstract] Cash paid for interest, net of capitalized interest of $20,403 and $18,901 as of March 31, 2020 and 2019, respectively Interest Paid, Excluding Capitalized Interest, Operating Activities Capitalized interest Interest Costs Capitalized Cash paid for amounts included in the measurement of ground lease liabilities Operating Lease, Payments NON-CASH INVESTING TRANSACTIONS: Noncash Investing Activities [Abstract] Noncash Investing Activities. Accrual for expenditures for operating properties and development properties Capital Expenditures Incurred but Not yet Paid Tenant improvements funded directly by tenants Tenant improvements funded directly by tenants to third parties The amount of cash paid directly to third parties by tenants for tenant improvements owned by the Company. Initial measurement of operating right of use ground lease assets Operating Lease, Right-of-Use Asset Initial measurement of operating ground lease liabilities Operating Lease, Liability NON-CASH FINANCING TRANSACTIONS: Noncash Financing Activities [Abstract] Accrual of distributions payable to common unitholders (Notes 6 and 15) Common Stockholders And Unitholders Dividends And Distributions Declared But Not Paid Dividends and distributions declared but not paid to common stockholders and common unitholders. Consolidation policy Consolidation, Policy [Policy Text Block] Basis of accounting Basis of Accounting, Policy [Policy Text Block] New accounting pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Equity [Abstract] Stockholders' Equity of the Company Stockholders' Equity Note Disclosure [Text Block] Fair Value Measurements and Disclosures Fair Value Disclosures [Text Block] Statement of Stockholders' Equity [Abstract] Dividends declared per common share and common unit (in dollars per share) Common Stock, Dividends, Per Share, Declared Schedule of contractual expiration dates for ground leases Lessee, Operating Leases [Text Block] Schedule of future minimum rental repayments for ground leases Lessee, Operating Lease, Liability, Maturity [Table Text Block] Schedule of Common Units outstanding Redeemable Noncontrolling Interest [Table Text Block] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Measurement Frequency [Axis] Measurement Frequency [Axis] Measurement Frequency [Domain] Measurement Frequency [Domain] Fair value, measurements, recurring [Member] Fair Value, Recurring [Member] Fair value (Level 1) [Member] Fair Value, Inputs, Level 1 [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Assets and Liabilities Reported at Fair Value Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Abstract] Marketable securities Assets, Fair Value Disclosure Fair value adjustment of marketable securities and deferred compensation plan liability Fair Value, Adjustment Disclosure [Abstract] Net (loss) gain on marketable securities Marketable Securities, Gain (Loss), Excluding Other-than-temporary Impairment Loss Noncontrolling Interest [Abstract] Noncontrolling Interest [Table] Noncontrolling Interest [Table] Noncontrolling Interest [Line Items] Noncontrolling Interest [Line Items] Common units outstanding held by common limited partners (in units) Number of trading days Debt Instrument, Convertible, Threshold Trading Days Aggregate value upon redemption of outstanding noncontrolling common units Redeemable Noncontrolling Interest, Equity, Common, Fair Value Organization, Ownership and Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure and Significant Accounting Policies [Text Block] Dividends declared per common unit (in dollars per unit) Distributions Per Limited Partnership and General Partnership Unit, Outstanding, Basic Share-based Payment Arrangement [Abstract] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Title of Individual [Axis] Title of Individual [Axis] Title of Individual [Domain] Title of Individual [Domain] One Participant [Member] One Participant [Member] One Participant [Member] Award Type [Axis] Award Type [Axis] Award Type [Domain] Award Type [Domain] Performance-Based RSUs [Member] Performance-Based RSUs [Member] Performance-Based RSUs [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Expected share price volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Risk-free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Fair value per share on valuation date (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Schedule of share-based payment award, restricted stock units, valuation assumptions Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Schedule of supplemental cash flows Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Reconciliation of cash and cash equivalents and restricted cash Schedule of Cash and Cash Equivalents [Table Text Block] Reconciliation of cash and cash equivalents and restricted cash Restrictions on Cash and Cash Equivalents [Table Text Block] Rental income Operating Lease, Lease Income [Table Text Block] Future contractual minimum rent under operating leases Lessor, Operating Lease, Payments to be Received, Maturity [Table Text Block] Unsecured term loan facility, unsecured senior notes and secured debt [Member] Unsecured Term Loan Facility, Unsecured Senior Notes and Secured Debt [Member] Unsecured Term Loan Facility, Unsecured Senior Notes and Secured Debt [Member] Unsecured senior notes [Member] Stated debt maturities and scheduled amortization payments Long-term Debt, Fiscal Year Maturity [Abstract] Remaining 2020 Long-term Debt, Maturities, Repayments of Principal, Remainder of Fiscal Year 2021 Long-term Debt, Maturities, Repayments of Principal in Year Two 2022 Long-term Debt, Maturities, Repayments of Principal in Year Three 2023 Long-term Debt, Maturities, Repayments of Principal in Year Four 2024 Long-term Debt, Maturities, Repayments of Principal in Year Five 2025 Long-term Debt, Maturities, Repayments of Principal in Year Six Long-term Debt, Maturities, Repayments of Principal in Year Six Thereafter Long-term Debt, Maturities, Repayments of Principal after Year Five Total debt Long-term Debt, Gross Unamortized deferred financing costs Unamortized Debt Issuance Expense Unamortized discount Debt Instrument, Unamortized Discount Cover [Abstract] Entities [Table] Entities [Table] Entity Information [Line Items] Entity Information [Line Items] Document Type Document Type Document Quarterly Report Document Quarterly Report Document Period End Date Document Period End Date Document Transition Report Document Transition Report Entity File Number Entity File Number Entity Registrant Name Entity Registrant Name Entity Incorporation, State Code Entity Incorporation, State or Country Code Entity Tax Identification Number Entity Tax Identification Number Entity Address, Address Line One Entity Address, Address Line One Entity Address, Address Line Two Entity Address, Address Line Two Entity Address, City or Town Entity Address, City or Town Entity Address, State or Province Entity Address, State or Province Entity Address, Postal Zip Code Entity Address, Postal Zip Code City Area Code City Area Code Local Phone Number Local Phone Number Title of 12(b) Security Title of 12(b) Security Security Exchange Name Security Exchange Name Trading Symbol Trading Symbol Title of 12(g) Security Title of 12(g) Security Entity Current Reporting Status Entity Current Reporting Status Entity Interactive Data Current Entity Interactive Data Current Entity Filer Category Entity Filer Category Entity Emerging Growth Company Entity Emerging Growth Company Entity Small Business Entity Small Business Entity Shell Company Entity Shell Company Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Income Statement [Abstract] REVENUES Revenues [Abstract] Rental income (Note 8) Operating Lease, Lease Income Other property income Revenue from Contract with Customer, Including Assessed Tax Total revenues Revenues EXPENSES Operating Expenses [Abstract] Property expenses Other Cost and Expense, Operating Real estate taxes Real Estate Tax Expense Ground leases (Note 9) Operating Lease, Expense General and administrative expenses General and Administrative Expense Leasing costs Operating Lease, Cost Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Total expenses Operating Expenses OTHER (EXPENSES) INCOME Nonoperating Income (Expense) [Abstract] Interest income and other net investment (loss) gain (Note 10) Interest Income And Other Net Investment Gain (Loss) Income derived from investments in debt and equity securities and on cash and cash equivalents and the net total realized and unrealized gain (loss) included in earnings for the period as a result of selling or holding marketable securities categorized as trading. Interest income represents earnings which reflect the time value of money or transactions in which the payments are for the use or forbearance of money. Dividend income represents a distribution of earnings to shareholders by investee companies. Interest expense (Note 3) Interest Expense Total other (expenses) income Nonoperating Income (Expense) NET INCOME Net income attributable to noncontrolling common units of the Operating Partnership Noncontrolling Interest in Net Income (Loss) Operating Partnerships, Redeemable Net income attributable to noncontrolling interests in consolidated property partnerships Net Income (Loss) Attributable to Noncontrolling Interest in Consolidated Subsidiary Net Income (Loss) Attributable to Noncontrolling Interest in Consolidated Subsidiary Total income attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest NET INCOME AVAILABLE TO COMMON STOCKHOLDERS (UNITHOLDERS) Net Income (Loss) Available to Common Stockholders, Basic Net income available to common stockholders per share – basic (in dollars per share) Net income available to common stockholders per share – diluted (in dollars per share) Weighted average common shares outstanding – basic (in shares) Weighted average common shares outstanding – diluted (in shares) Net Income Available to Common Stockholders Per Share of the Company Prepaid Expenses and Other Assets, Net Other Assets Disclosure [Text Block] Noncontrolling Interests on the Company's Consolidated Financial Statements Noncontrolling Interest Disclosure [Text Block] Schedule of Sale of Stock Schedule of Sale of Stock by Subsidiary or Equity Method Investee Disclosure [Table Text Block] Line of Credit Facility [Table] Line of Credit Facility [Table] Revolving credit facility [Member] Revolving Credit Facility [Member] $150 Million Term Loan Facility [Member] One Hundred Fifty Million Term Loan Facility [Member] One Hundred Fifty Million Term Loan Facility [Member] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] London Interbank Offered Rate (LIBOR) [Member] London Interbank Offered Rate (LIBOR) [Member] Terms of the Credit Facility Line of Credit Facility [Abstract] Outstanding borrowings Long-term Line of Credit Remaining borrowing capacity Line of Credit Facility, Remaining Borrowing Capacity Total borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Interest rate (percent) Line of Credit Facility, Interest Rate at Period End Facility fee-annual rate (percent) Line of Credit Facility, Commitment Fee Percentage Undrawn facility fee-annual rate (percent) Line of Credit Facility, Unused Capacity, Commitment Fee Percentage Contingent additional borrowings Debt Instrument, Contingent Additional Borrowings Debt Instrument, Contingent Additional Borrowings Variable rate (percent) Debt Instrument, Basis Spread on Variable Rate Unamortized deferred financing costs Prepaid Expense and Other Assets [Abstract] Prepaid Expense and Other Assets [Abstract] Furniture, fixtures and other long-lived assets, net Furniture and Fixtures, Gross Prepaid expenses Prepaid Expense Note receivable Accounts and Financing Receivable, after Allowance for Credit Loss Total prepaid expenses and other assets, net Prepaid Expense and Other Assets Valuation allowance Allowance for Doubtful Accounts, Premiums and Other Receivables Common Stock [Member] Common Stock [Member] Additional Paid-in Capital [Member] Additional Paid-in Capital [Member] Distributions in Excess of Earnings [Member] Accumulated Distributions in Excess of Net Income [Member] Total Stockholders' Equity [Member] Parent [Member] Noncontrolling Interests [Member] Noncontrolling Interest [Member] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance (in shares) Beginning balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Opening adjustment to Distributions in Excess of Earnings upon adoption of ASC 842 Cumulative Effect of New Accounting Principle in Period of Adoption Issuance of common stock (in shares) Stock Issued During Period, Shares, New Issues Issuance of common stock (Note 4) Stock Issued During Period, Value, New Issues Issuance of share-based compensation awards Shares Issued, Value, Share-based Payment Arrangement, after Forfeiture Non-cash amortization of share-based compensation (Note 7) APIC, Share-based Payment Arrangement, Increase for Cost Recognition Settlement of restricted stock units for shares of common stock (in shares) Stock Issued During Period, Shares, Restricted Stock Award, Gross Settlement of restricted stock units for shares of common stock Stock Issued During Period, Value, Restricted Stock Award, Gross Repurchase of common stock, stock options and restricted stock units (in shares) Stock Repurchased and Retired During Period, Shares Repurchase of common stock, stock options and restricted stock units Stock Repurchased and Retired During Period, Value Exchange of common units of the Operating Partnership (in shares) Stock Issued During Period, Shares, Conversion of Units Exchange of common units of the Operating Partnership Stock Issued During Period, Value, Conversion of Units Distributions to noncontrolling interests in consolidated property partnerships Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Adjustment for noncontrolling interest Adjustments to Additional Paid in Capital, Other Dividends declared per common share and common unit Dividends, Common Stock Ending balance (in shares) Ending balance Restricted Stock Units (RSUs) [Member] Restricted Stock Units (RSUs) [Member] Market Measure-Based Restricted Stock Units (RSUs) [Member] Market Measure-Based Restricted Stock Units (RSUs) [Member] Market Measure-Based Restricted Stock Units (RSUs) [Member] Time-Based Restricted Stock Units (RSUs) [Member] Time-Based Restricted Stock Units (RSUs) [Member] Time-Based Restricted Stock Units (RSUs) [Member] Time-Based RSUs [Member] Time-Based RSUs [Member] Time-Based RSUs [Member] Time-Based Restricted Stock Units (RSUs), Grant [Member] Time-Based Restricted Stock Units (RSUs), Grant [Member] Time-Based Restricted Stock Units (RSUs), Grant [Member] Number of share-based incentive compensation plans Share-based Compensation Arrangement by Share-based Payment Award, Number of Plans Share-based Compensation Arrangement by Share-based Payment Award, Number of Plans Effective registration shares (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Number of shares available for grant (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Number of shares granted in period (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Vesting, achievement of pre-set FFO per share goals, percentage of RSUs Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting, Criteria Three Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting, Criteria Three Vesting, Average debt to EBIDTA ratio, percentage of RSUs Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting, Criteria One Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting, Criteria One Vesting, Market measure, percentage of RSUs Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting, Criteria Two Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vesting, Criteria Two Number of shares issuable per RSU Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Ratio Shares Granted per Unit Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Ratio Shares Granted per Unit Share price Share Price Remaining expected life, including future volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term, Doubled Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term, Doubled Performance period Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Fair value RSUs granted Share-based Compensation Arrangement By Share-based Payment Award, Equity Instruments Other Than Options, Grants In Period, Grant Date Fair Value The total fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans. Number of installments Share-based Compensation Arrangement by Share-based Payment, Installments Share-based Compensation Arrangement by Share-based Payment, Installments Right to receive number of shares (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Share Rights Share-based Compensation Arrangement by Share-based Payment Award, Share Rights Share-based compensation expense Share-based Payment Arrangement, Expense Share-based compensation expense capitalized Share-based Payment Arrangement, Amount Capitalized Share-based compensation not yet recognized Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Share-based compensation not yet recognized period of recognition Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Summary of real estate properties Schedule of Real Estate Properties [Table Text Block] Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Table] Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Table] Consolidated Entities [Axis] Consolidated Entities [Axis] Consolidated Entities [Domain] Consolidated Entities [Domain] Variable Interest Entity, Primary Beneficiary [Member] Variable Interest Entity, Primary Beneficiary [Member] Kilroy Realty Finance, Inc. [Member] Kilroy Realty Finance, Inc. [Member] Kilroy Realty Finance, Inc. [Member] 101 First LLC and 303 Second LLC [Member] 101 First LLC and 303 Second LLC [Member] 101 First LLC and 303 Second LLC [Member] Redwood LLC [Member] Redwood LLC [Member] Redwood LLC [Member] Finance Partnership [Member] Finance Partnership [Member] Finance Partnership [Member] Investment Type [Axis] Investment Type [Axis] Investments [Domain] Investments [Domain] Real estate investment [Member] Real Estate Investment [Member] Development properties [Member] Development Properties [Member] Development Properties [Member] Office properties owned by consolidated property partnerships [Member] Office Properties Owned by Consolidated Property Partnerships [Member] Office Properties Owned by Consolidated Property Partnerships [Member] Development sites [Member] Development Sites [Member] Development Sites [Member] Development Project [Member] Development Project [Member] Development Project [Member] Properties and development projects [Member] Properties and Development Projects [Member] Properties and Development Projects [Member] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] San Francisco, California [Member] San Francisco, California [Member] San Francisco, California [Member] San Diego, California [Member] San Diego, California [Member] San Diego, California [Member] Washington [Member] WASHINGTON Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] Consolidation, Less than Wholly Owned Subsidiary, Parent Ownership Interest, Effects of Changes, Net [Line Items] Lease-up properties occupancy percentage Lease-Up Properties, Maximum Stabilized Occupancy, Percentage Lease-Up Properties, Maximum Stabilized Occupancy, Percentage Lease-up properties occupancy duration Lease-Up Properties, Maximum Stabilized Occupancy, Duration Lease-Up Properties, Maximum Stabilized Occupancy, Duration Number of properties Area of undeveloped land Area of Land Property ownership percentage Property Ownership Percentage Property Ownership Percentage Number of property partnerships Number of Property Partnerships Number of Property Partnerships Number of VIEs Variable Interest Entity, Number of Entities Variable Interest Entity, Number of Entities Company owned general partnership interest Noncontrolling Interest, Ownership Percentage by Parent Number of entities established Number Of Entities Number Of Entities Common general partnership interest in the Finance Partnership (percentage) Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest Assets Assets Liabilities Liabilities Noncontrolling interest in VIE Noncontrolling Interest in Variable Interest Entity Rentable square feet Schedule of Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Table] Schedule of Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Table] Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items] Numerator: Basic and diluted net loss income available to common unitholders [Abstract] Basic and diluted net (loss) income available to common unitholders. Net income attributable to Kilroy Realty, L.P. Allocation to participating securities Effect of dilutive securities (in units) Basic earnings per unit: Diluted earnings per unit: Future contractual minimum rent under operating lease Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract] Remaining 2020 Lessor, Operating Lease, Payments to be Received, Remainder of Fiscal Year 2021 Lessor, Operating Lease, Payments to be Received, Two Years 2022 Lessor, Operating Lease, Payments to be Received, Three Years 2023 Lessor, Operating Lease, Payments to be Received, Four Years 2024 Lessor, Operating Lease, Payments to be Received, Five Years 2025 Lessor, Operating Lease, Payments to be Received, Six Years Lessor, Operating Lease, Payments to be Received, Six Years Thereafter Lessor, Operating Lease, Payments to be Received, After Year Six Lessor, Operating Lease, Payments to be Received, After Year Six Total Lessor, Operating Lease, Payments to be Received Share-Based Compensation Share-based Payment Arrangement [Text Block] Supplemental Cash Flow Information of the Operating Partnership Cash Flow, Supplemental Disclosures [Text Block] Capitalized Interest and Loan Fees [Table] Capitalized Interest and Loan Fees [Table] Capitalized Interest and Loan Fees [Table] Capitalized Interest and Loan Fees [Line Items] Capitalized Interest and Loan Fees [Line Items] [Line Items] for Capitalized Interest and Loan Fees [Table] Gross interest expense Interest Costs Incurred Capitalized interest and deferred financing costs Interest Costs Capitalized Adjustment Interest expense SUPPLEMENTAL CASH FLOWS INFORMATION: Cash paid for interest, net of capitalized interest of $20,403 and $18,901 as of March 31, 2020 and 2019, respectively Cash paid for amounts included in the measurement of ground lease liabilities NON-CASH INVESTING TRANSACTIONS: Accrual for expenditures for operating properties and development properties Tenant improvements funded directly by tenants NON-CASH FINANCING TRANSACTIONS: Accrual of dividends and distributions payable to common stockholders and common unitholders (Notes 4 and 15) Exchange of common units of the Operating Partnership into shares of the Company’s common stock Conversion of Stock, Amount Converted Partners' Capital [Member] Partners Capital Common Unit [Member] Partners Capital Common Unit. Dividends, Common Stock Increase (Decrease) in Partners' Capital [Roll Forward] Beginning balance (in units) Partners' Capital Account, Units Beginning balance Partners' Capital, Including Portion Attributable to Noncontrolling Interest Opening adjustment to Partners’ Capital upon adoption of ASC 842 (Note 1) Issuance of common units (in units) Partners' Capital Account, Units, Sold in Public Offering Issuance of common units (Note 4) Partners' Capital Account, Public Sale of Units Issuance of share-based compensation awards Partners' Capital Account, Unit-based Payment Arrangement, Amount Non-cash amortization of share-based compensation (Note 7) Settlement of restricted stock units (in units) Settlement of restricted stock units Repurchase of common units, stock options and restricted stock units (in units) Partners' Capital Account, Units, Treasury Units Purchased Repurchase of common units, stock options and restricted stock units Partners' Capital Account, Treasury Units, Purchased Distributions to noncontrolling interests in consolidated property partnerships Dividends declared per common unit General Partners' Capital Account, Period Distribution Amount Ending balance (in units) Ending balance Minimum commitment under our ground leases Lessee, Operating Lease, Liability, Payment, Due [Abstract] Remaining 2020 Lessee, Operating Lease, Liability, Payments, Remainder of Fiscal Year 2021 Lessee, Operating Lease, Liability, Payments, Due Year Two 2022 Lessee, Operating Lease, Liability, Payments, Due Year Three 2023 Lessee, Operating Lease, Liability, Payments, Due Year Four 2024 Lessee, Operating Lease, Liability, Payments, Due Year Five 2025 Lessee, Operating Lease, Liability, Payments, Due Year Six Lessee, Operating Lease, Liability, Payments, Due Year Six Thereafter Lessee, Operating Lease, Liability, Payments, Due After Year Six Lessee, Operating Lease, Liability, Payments, Due After Year Six Total undiscounted cash flows Lessee, Operating Lease, Liability, Payments, Due Present value discount Lessee, Operating Lease, Liability, Undiscounted Excess Amount Ground lease liabilities Period after which ground lease rentals are adjusted based on fair market value and the Consumer Price Index Period for Ground lease rentals adjustment Period for Ground lease rentals adjustment. Annual ground lease rental obligations limit Annual Ground Lease Rental Obligations, Maximum Maximum annual ground lease rental obligations. Average annual percentage rent for previous five years (percent) Ground Lease, Minimum Rent Increase, Percentage of Annual Percentage Rent Ground Lease, Minimum Rent Increase, Percentage of Annual Percentage Rent for the previous 5 years Previous period included in average annual rent percentage for five-year increases Ground Lease, Previous Period Included in Average Annual Rent Percentage Ground Lease, Previous Period Included in Average Annual Rent Percentage Duration of ground lease prior to increase ten years Ground Lease, Minimum Rent Increase, Period of Increase Two Ground Lease, Minimum Rent Increase, Period of Increase Two Average annual percentage rent for previous ten years (percent) Ground Lease, Minimum Rent Increase, Percentage of Annual Percentage Rent Two Ground Lease, Minimum Rent Increase, Percentage of Annual Percentage Rent Two Previous period included in average annual rent percentage for ten-year increases Ground Lease, Previous Period Included in Average Annual Rent Percentage, Rent Two Ground Lease, Previous Period Included in Average Annual Rent Percentage, Rent Two Percentage rent increase every five years Ground Lease, Minimum Rent Increase, Five Years, Percentage of Annual Percentage Rent Ground Lease, Minimum Rent Increase, Five Years, Percentage of Annual Percentage Rent ASSETS Assets [Abstract] REAL ESTATE ASSETS: Real Estate Investment Property, Net [Abstract] Land and improvements Land and Land Improvements Buildings and improvements Investment Building and Building Improvements Undeveloped land and construction in progress Undeveloped Land and Construction in Progress The carrying amount of land and buildings available for development and redevelopment. Additionally, the current amount of expenditures for a real estate project that has not yet been completed. Total real estate assets held for investment Real Estate Investment Property, at Cost Accumulated depreciation and amortization Real Estate Investment Property, Accumulated Depreciation Total real estate assets held for investment, net Real Estate Investment Property, Net CASH AND CASH EQUIVALENTS (Note 4) RESTRICTED CASH MARKETABLE SECURITIES (Note 10) Debt Securities, Trading, and Equity Securities, FV-NI CURRENT RECEIVABLES, NET Accounts Receivable, after Allowance for Credit Loss DEFERRED RENT RECEIVABLES, NET Deferred Rent Receivables, Net DEFERRED LEASING COSTS AND ACQUISITION-RELATED INTANGIBLE ASSETS, NET Deferred Leasing Costs And Acquisition Related Intangible Assets Net This element represents (1) costs incurred by the lessor that are (a) costs to originate a lease incurred in transactions with independent third parties that (i) result directly from and are essential to acquire that lease and (ii) would not have been incurred had that leasing transaction not occurred and (b) certain costs directly related to specified activities performed by the lessor for that lease. Those activities are: evaluating the prospective lessee's financial condition; evaluating and recording guarantees, collateral, and other security arrangements; negotiating lease terms; preparing and processing lease documents; and closing the transaction; (2) the identifiable intangible asset established upon acquisition based on a favorable difference between the terms of an acquired lease and the current market terms for that lease at the acquisition date; and (3) the amount of value allocated by a lessor (acquirer) to lease agreements which exist at acquisition of a leased property. This element is net of accumulated amortization. RIGHT OF USE GROUND LEASE ASSETS (Note 9) PREPAID EXPENSES AND OTHER ASSETS, NET (Note 2) TOTAL ASSETS LIABILITIES AND EQUITY Liabilities and Equity [Abstract] LIABILITIES: Liabilities [Abstract] Secured debt, net (Notes 3 and 10) Secured Debt Unsecured debt, net (Notes 3, 10 and 15) Unsecured Debt Unsecured line of credit (Notes 3 and 10) Accounts payable, accrued expenses and other liabilities Accounts Payable and Accrued Liabilities Ground lease liabilities (Note 9) Accrued dividends and distributions (Note 15) Dividends Payable Deferred revenue and acquisition-related intangible liabilities, net Disposal Group, Including Discontinued Operation, Deferred Revenue And Acquisition Related Intangible Liabilities Disposal Group, Including Discontinued Operation, Deferred Revenue And Acquisition Related Intangible Liabilities Rents received in advance and tenant security deposits Disposal Group, Including Discontinued Operation, Advance Rent, Including Tenant Security Deposits Disposal Group, Including Discontinued Operation, Advance Rent, Including Tenant Security Deposits Total liabilities COMMITMENTS AND CONTINGENCIES (Note 9) Commitments and Contingencies EQUITY: Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Stockholders’ Equity (Note 4): Stockholders' Equity Attributable to Parent [Abstract] Common stock, $.01 par value, 150,000,000 shares authorized, 115,067,924 and 106,016,287 shares issued and outstanding, respectively Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Distributions in excess of earnings Retained Earnings (Accumulated Deficit) Total stockholders’ equity Stockholders' Equity Attributable to Parent Noncontrolling Interests (Notes 1 and 5): Noncontrolling Interest Items [Abstract] Common units of the Operating Partnership Noncontrolling Interest in Operating Partnerships Noncontrolling interests in consolidated property partnerships Total noncontrolling interests Stockholders' Equity Attributable to Noncontrolling Interest Total equity Common units, 115,067,924 and 106,016,287 held by the general partner and 2,021,287 and 2,023,287 held by common limited partners issued and outstanding, respectively (Note 6) General Partners' Capital Account Noncontrolling interests in consolidated property partnerships and subsidiaries (Note 1) Partners' Capital Attributable to Noncontrolling Interest Total capital TOTAL LIABILITIES AND EQUITY (CAPITAL) Liabilities and Equity Fixed lease payments Operating Lease, Lease Income, Lease Payments Variable lease payments Operating Lease, Variable Lease Income Collectibility (reversals) recoveries (1) Operating Lease Income, Adjustments Operating Lease Income, Adjustments Total rental income Reversal of revenue related to cumulative impact of transitioning certain tenants to cash basis of revenue recognition Operating Lease Income, Adjustments, Transitioning Tenants to Cash Basis Operating Lease Income, Adjustments, Transitioning Tenants to Cash Basis 2018 At-The-Market Program [Member] 2018 At-The-Market Program [Member] 2018 At-The-Market Program [Member] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] Sale of Stock [Axis] Sale of Stock [Axis] Sale of Stock [Domain] Sale of Stock [Domain] Forward equity sale [Member] Forward Equity Sale [Member] Forward Equity Sale [Member] Forward equity offering, numbers of shares authorized (in shares) Forward Contract Indexed to Issuer's Equity, Shares Forward equity offering, value of shares offered Forward Contract Indexed to Issuer's Equity, Settlement Alternatives, Shares, at Fair Value Forward equity offering price per share (in dollars per share) Forward Contract Indexed to Issuer's Equity, Forward Rate Per Share At the market stock offering aggregate gross sales price of common stock At Market Stock Aggregate Gross Sales Price of Common Stock At Market Stock Aggregate Gross Sales Price of Common Stock Sale of stock, shares available for sale (in shares) Sale of Stock, Shares Available for Sale Sale of Stock, Shares Available for Sale Price per share (in dollars per share) Sale of Stock, Price Per Share At the market stock offering remaining amount available for issuance At Market Stock Offering Program Remained Available For Issuance At Market stock offering program remained available for issuance. Number of shares issued (in shares) Sale of Stock, Number of Shares Issued in Transaction Proceeds from issuance of stock Proceeds from Issuance of Common Stock Aggregate net proceeds after selling commissions Sale of Stock, Consideration Received on Transaction Supplemental Cash Flow Information of the Company